1. Field of the Invention
This invention relates to a solid-fuel pellet thrust and control actuation system (CAS) for providing command authority to maneuver a flight vehicle over an entire vehicle speed range encompassing both the subsonic and supersonic Mach numbers and within the atmosphere and exo-atmosphere.
2. Description of the Related Art
Flight vehicles such as self-propelled missiles, gun or tube launched guided projectiles, kinetic interceptors and unmanned aerial vehicles require command authority, to maneuver the vehicle to perform guidance and attitude control. Each of these vehicles may operate over a speed range encompassing both subsonic and supersonic Mach numbers and within the atmosphere and exo-atmosphere during a single mission. The differing speed and atmospheric conditions present different problems for effectively maneuvering the vehicle under volume, weight and cost constraints imposed by the vehicle and mission.
One approach used in a majority, if not all missile products employs a Control Actuation System (CAS) for guidance to the target. Typically the CAS employs a set of four fin control surfaces actuated by individual servo motors. Actuation of the fin control surfaces into the onrushing free stream produces drag and directional forces to maneuver the vehicle. Control surfaces are effective at supersonic speeds above Mach 1 in atmosphere where sufficient drag and force is produced to quickly maneuver the vehicle. However at subsonic speeds in atmosphere the amount of drag and force is relatively small and maneuverability is limited. In the exo-atmosphere, actuation of the fin control surface is wholly ineffective because no drag or force is produced. Furthermore the servo motors are very expensive, up to 25% of the missile cost, and have reliability issues related to the moving parts of the servo motor being exposed to ver high g loads at launch.
Another approach is to use divert thrusters (or attitude thrusters) that expel stored or combustion gas through a nozzle producing a force to directly maneuver the vehicle. A liquid-fuel divert thruster system includes one or more liquid or gas storage tanks and a regulator valve to mix and a combustion chamber to burn the liquid or gas propellants. The liquid propellant configurations are comprised of either monopropellant systems or bipropellant systems where the bipropellant system contains a fuel and an oxidizer. Liquid-fuel has the advantage that the amount of thrust can be continuously varied, started and stopped, and may be less expensive than servo motors. However, these systems are large and heavy. Liquid propellant divert thruster systems are used in space-based platforms such as satellites and kinetic kill-vehicles. A solid-fuel propellant system is more light weight and less complicated but once ignited burns until completion where all the solid fuel has been consumed. A variant on the solid-fuel propellant system are “pyrotechnic thrusters” or “poppers” that generate a thrust pulse, Pyrotechnic thrusters can be effectively employed in the subsonic regime of the vehicle flight in atmosphere and also exo-atmospheric.
The liquid or solid-fuel propellant divert thrusters are not as effective as control surfaces such as fins at supersonic speeds in atmosphere. The on rushing high speed free stream relative to the vehicle has such a high degree of momentum in conjunction with the high vehicle momentum that the divert jet thrust is only marginally effective unless unrealistically large divert thrusters are employed. A divert thruster system would have to burn for a long time in order to maneuver. Long burn times at supersonic speeds create a vehicle packaging problem because of the volume requirements imposed by the amount of propellant required. The ability of the vehicle to maneuver quickly, which is critical in many military applications, is also limited at supersonic speeds.